Orbital and Millennial-Scale Cycles Through the Hirnantian (Late Ordovician) in Southern China

The Hirnantian period, making the end of the Ordovician with significant mass extinctions and large ice-sheets, is a critical interval for studying paleoclimate variations. This research represents the first cyclostratigraphic study of this period, utilizing high-resolution (1 mm sampling rate) geochemical data from the similar to 7-m thick SH-1 drill core, capturing the latest Ordovician glaciation. Our analysis identifies the presence of Milankovitch cycles with periods of 17-21, similar to 33, and similar to 100-kyr, suggesting an optimal sedimentation rate of 3.1 m/Myr. Notably, we detected signals of millennial-scale variability, aligning with the similar to 1.5-kyr Dansgaard-Oeschger and similar to 2.4-kyr Hallstatt heliomagnetic cycles, even in deposits lacking visible laminae alternation. This finding bolsters the hypothesis of an external origin for these millennial-scale features. Additionally, our reconstruction of sea-level variations, using principal component analysis and sedimentary noise modeling, reveals two intervals of sea-level fall and one sea-level rise, linked to an astronomical forcing cycle of similar to 1.2-Myr. The obliquity band power-total power ratios correspond to similar to 1.2-Myr periodicities for s4-s3 term. The synchronization of similar to 1.2-Myr cycle minimum with a sea-level drop (low PC1 value) suggests that glacio-eustatic variations were influenced by similar to 1.2-Myr obliquity modulation cycles. This research enhances our understanding of glacio-eustasy during the latest Ordovician from an astronomical perspective, offering valuable insights into the interplay between orbital cycles and Earth's paleoclimate. Millennial-scale cycles have been detected based on five high-resolution proxy series Millennial-scale cycle preserved in the Hirnantian was linked to the D-O and Hallstatt cycle similar to 1.2-Myr PC1 filter revealed one rise and two falls of sea-level during Hirnantian